The following features of heterocyst differentiation in the nitrogen-fixing blue-green alga Nostoc muscorum will be studied: DNA synthesis modification, and degradation in developing cells; the pattern of protein synthesis in developing cells; protease action in developing cells; membrane reorganization in developing cells; biosynthetic capacities of isolated heterocysts; and the isolation of developmental mutants of Nostoc. BIBLIOGRAPHIC REFERENCE: Haselkorn, R. and Rouviere-Yaniv, J. Cyanobacterial DNA-binding protein related to E. coli HU. Proc. Nat. Acad. Sci. USA, 73, 1917-1920 (1976).